In mobile communication networks, there is always a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the mobile communication network is deployed.
The demand for spectrum is increasing and frequency bands (such as frequency bands below 1 GHz) are becoming more congested, especially in densely populated urban centers. Spectrum sharing technologies enable the spectrum to be shared between different radio access technologies (RATs). In general terms, spectrum sharing encompasses several techniques; administrative, technical and market based. Spectrum can be shared in several dimensions; time, space and geography. Examples of technologies for spectrum sharing include, but are not limited to inband sharing, leasing and spectrum trading, and use of unlicensed spectrum commons combined with the use of low power radios or advanced radio technologies including ultra-wideband and multi-modal radios.
FIG. 1 schematically illustrates an example of spectrum sharing between a first RAT (denoted RAT-1) allocating carriers 1a and second RAT (denoted RAT-2) allocating carriers 1b; when the load of RAT-1 is high and the load of RAT-2 is low, a bandwidth reallocation is initiated and one carrier of RAT-2 is reallocated to RAT-1. The potential user throughput gain in this example (going from 2 to 3 carriers) is 50%. It may be necessary to deploy radio base stations (RBS), also referred to as network nodes (NN), that can handle more than one RAT simultaneously to enable spectrum sharing. Such an RBS or NN that handles more than one RAT simultaneously may be referred to as a mixed mode multi standard RBS or NN.
FIG. 2 schematically illustrates a second example of spectrum sharing between a first RAT and a second RAT. The top part of the figure illustrates the total sector load 2a, 2b per RAT and the bottom part illustrates the number of carriers 2c, 2d, per RAT. A first RAT is associated with cell load 2a and the number of carriers 2c; a second RAT is associated with cell load 2b and the number of carriers 2d. The cell load 2a, 2b is constantly measured for the RATs. According to the illustrative example, when the load of one RAT is 75% (In FIG. 2 denoted “High_threshold”) of the maximum load, and the other RAT has lower load than 25% (In FIG. 2 denoted “Low_threshold”), a spectrum reallocation is performed (in FIG. 2 denoted “Reallocate”). In this example the first RAT associated with cell load 2a is given another carrier (in total 3 carriers). When the cell load 2b once again is above 25%, another reallocation is performed; this time reallocating a carrier back to the second RAT.
However, there is still a need for an improved spectrum sharing between different RATs.